Ducati 1981 900 SS Dellortto help, please!

[morison]

40's were always over kill on Super Sports. They use similar jetting as 36's and probably 32's up to legal speeds. The only real benefit is when your red lining the thing i.e full throttle racing.
Having said that they were good fun apart from fouling plugs through traffic. I just stayed away from traffic. The last 900 SS I had used to get phenomenal fuel consumption with the 40's. On a trip back from the Snowies, two up and sitting between 130kph to 160kph I was getting 70 mpg, a shade under 25km/litre. My Lav gets, at best, 18-19 km/litre. Maybe I don't thrash it enough?

Nice bikes SS's especially when you convert to low rise touring bars, a 750 Sport instrument binnacle and 860 GTS spring type headlight clamps. It's a straight swap. Higher bars and rear sets are really comfortable.

 

[wdietz186]

Actually, Using a richer slide will help the off idle stumble.I've seen a few 50/1 slides in good running 900s
The problem is they would be kind of an expensive experiment.

 

[Steve G.]

thanks all...

so in summary, best  solution likely  upgraded .

Or trade up to a....L....  

Hi Tippie

my buddy with the Ducati 900 SS also has a very nice early drum brake Laverda 750, I went through the motor of the Laverda for him about two years ago, sorted the electrics, etc. He recently acquired the 900 SS from an estate, the previous owner was a Canadian military pilot who died in the crash of his military jet, very sad.

As for the Ducati 900 SS, it is refreshing to work on a bevel Ducati intended to be a regular rider, which this particular bike has not been for at least 15 years as it hasn't run correctly in at least that long...... the shops that have worked on this bike should be ashamed of themselves

I have it running quite well now, with some final dialing in to do after some further test riding to be done, the engine still bogs slightly just off idle on the transition, I am going to richen up the idle jet circuit just a bit more even though with the stupid 40 mm carbs it is already rich at idle. I think the thing would run much better with a pair of smaller carbs.

Paul LeClair

  You've got a bit of altitude there don't you Paul? Is that a secondary cause of the rich running?

  Steve

 

[Dellortoman]

   You've got a bit of altitude there don't you Paul?

At first glance I thought you'd written "attitude" 

I was wondering what Paul had done to warrant such a comment  ???

 

[Spub]

While it is a good idea to look at the stock settings on setting up a bevel, my experience has been you will always have a lot of trial and error before the best combination of jets and settings is arrived at. The first year 900s (1975) came with 40s that ran filterless (trumpets only) and had Contis. These generally ran 265 needle jets, K4 needle, 55 to 60 idles and 145-155 mains. Obviously adding pod filters or different exhausts would change the settings. The fuel mixture screw settings I set by ear, and very rarely were they the same or even close for the front and rear carb. Later models, such as the one you are working on, originally came with 32 Dellortos, airboxes and Laffranconi mufflers. Most owners of these later models chucked the Laffronconis and the airbox, put on Contis, and added 40s with trumpets or pod filters. 

The 40s suck a lot of air, and every 900 I have seen with 40s tended not to idle to well unless warmed up, some not to well even after that. Going down to 36 or 32 Dellortos improves not only this but also the "streetability" of the bike. Quite frankly, while there was some drop off in top end performance with the smaller carbs, I think the bike is much more rideable as a daily runner, and I did not think the drop off was significant enough to overcome the rideability gains....Of course, that being said, few people run them as "daily runners", and most much prefer the look of the trumpets and the 40s, since this is more in keeping with the racing heritage of the marque. I kept the 40s on my bike, kept the trumpets, wiped the slides off after every few rides to keep wear to a minimum and was running 150s, 58 idles, stock needle, slide and needle jet and I tinkered with the timing. After owning it for 5 years I was very satisfied with the set up, since I rode it only on weekends. It made good power, idled, and was one of the best bikes I have ever owned...damn I wished I hadn't sold it....